Indexing help needed

[astrocan]

After a considerable amount of unacceptable language I went and asked my son what was wrong. It is the usual problem with his gears, which keep skipping or missing.
We have both done a maintenance course and have a fair idea about indexing but we have both tried as many ways as we can think of and we cannot get them to run exactly right.
We can get it to change up smoothly then it will skip sprockets going down.
If it is skipping 4th we can adjust it out but only so that it now skips 3rd. The chain and changer are not that old but I am not sure how old the cassette is.
Son is 15 and I suspect that he is not as considerate toward his bike as he would have me believe so that may have something to do with it.
Does anyone have any ideas or suggestions?

 

[Dave5N]

Best to change cassette when you change the chain.

Have you checked the derrailleur is straight and the B screw adjusted right?

 

[swee'pea99]

Must admit I have real problems with this and I'm certainly nothing like an expert, but two tips that might help: first, lubrication in the cabling - dribble oil inside the housing, and check particularly where they go round under the bottom bracket. If there's any 'stickiness', it can cause problems in one direction, because you're strong enough to overcome it, but the spring in the mech that's pulling in the other direction isn't. Second, checkout bicycletutor.com - there's a good vid on adjusting indexed gears.

 

[gwhite]

This fault as described can be typical of a bent der hanger. Go to the rear of the machine and confirm that the rear der is perpendicular under the chosen sprocket. A more precise check can be done in a bike workshop with the appropriate tool.

 

[astrocan]

We will give those a go and let you know how we get on.
Thanks for the help.

 

[astrocan]

Have you checked the derrailleur is straight and the B screw adjusted right?

Judging by the language son has already checked the B screw and the F nut as well as the P washers.

 

[Marin Maniac]

I'm with the bent d hanger

 

[Deleted member 1258]

I'm with the bent d hanger

Sounds like that could be it, or its wear on the cassette, another possibility is worn pivot points on the rear mech, that can lead to the mech changing one way only. Its something I haven't come across recently, but I have lost two or three seven speed mechs to the problem in the past.